Mail Dog (1947)

Pluto must deliver mail to a remote outpost.

When a pilot has to turn back due to a severe storm, he drops the mail at a remote outpost where it can be delivered by dogsled. The falling mail pouch lands on Pluto, and he sets out to deliver it. He is continually delayed by a rabbit along the way, but in the end, the rabbit helps Pluto deliver the mail pouch.